Gas sensors, which comprise an emitter, a cuvette (test cell) as well as a detector, are known. In optical gas sensors, the emitter is a light source, e.g., a light bulb, which emits a broad spectrum of light waves, i.e., light waves having a plurality of different wavelengths. The cuvette is preferably an essentially closed space, in which the gas to be measured is located. The cuvette may comprise openings to the outside, which make possible an exchange of gas of the cuvette with an area surrounding the gas sensor. The detector is a light sensor, with which preferably an intensity of light, which reaches the detector, can be measured. In order to detect defined wavelengths of the light, bandpass filters are arranged upstream of the corresponding detectors. Such bandpass filters may be configured to let through one or more wavelengths.
The gas or gas mixture to be measured is introduced into the cuvette during the operation. For this, the cuvette may comprise one or more openings. Light waves emitted by the light source are more or less strongly absorbed by the respective gas depending on the concentration of the ingredients of the gas mixture, as well as on the absorption wavelengths. It is possible in this way to determine which wavelengths were absorbed and how strongly by the gas. Because of known specific absorption properties of different gases, a composition of the gas mixture can be determined from this result.
An optical gas sensor comprising a hollow cylindrical cuvette for holding the gas to be measured is known from DE 202 02 694 A1. A plane mirror on one side and a concave mirror on the other side are arranged at the cuvette in the longitudinal axial direction. The concave mirror comprises a plurality of recesses for accommodating a light bulb and a light wave detector. Light waves emitted by the light bulb are first repeatedly reflected between the plane mirror and the concave mirror until they reach the light wave detector. As a result of this, an optical path length, on which these light waves can be absorbed by the gas or gas mixture to be measured, is extended. Weakly absorbing gases can thus be measured better.
Such a gas sensor has especially the drawback that an arrangement of the light bulb and light wave detectors at the concave mirror can only be produced with great effort because of the curved surface of the concave mirror. Furthermore, a plurality of the light sources used in optical gas sensors have the drawback of emitting a relatively broad spectrum of light waves. Thus, not only are light waves emitted with wavelengths that are needed for measuring the gas concentration, but also light waves with wavelengths which are not of significance for measuring the gas concentration and have to be filtered out by a bandpass filter to avoid measuring errors. As a result, the efficiency of the optical gas sensor is adversely affected. In particular, light bulbs have, moreover, the drawback that a large percentage of electrical energy is converted into heat, which has to be dissipated as heat due to energy losses. This leads to an excessive energy consumption of the gas sensor and is especially disadvantageous for mobile applications, which are supplied with power via an internal power source, e.g., a battery. The life of the battery and thus the operating time of the mobile gas sensor are markedly reduced due to the increased power consumption.